The present invention relates to a tire condition monitoring apparatus and, more particularly, to a casing structure in a wireless-communication-type tire condition monitoring apparatus which enables tire conditions including the air pressure in a tire to be checked from the interior of a vehicle.
Snap-in valves in which a valve stem and rubber are formed integrally with each other under vulcanization conditions have been frequently used as vehicle tire valves. When a snap-in valve is mounted, an end portion of the valve stem is first passed through a valve hole from the inside of a wheel, with a valve cap screwed on the extreme end portion of the valve stem. The snap-in valve is then press-fitted in the valve hole. A sealing surface formed in a peripheral direction at the base end of the snap-in valve is thereby placed in the valve hole. As a result, the sealing surface adheres to the surface of the valve hole to maintain airtightness of the tire. (See Japanese Utility Model Publication No. 32-6 or a document from Japanese Standards Association “JIS Handbook, 2001, (18) Automobiles-Parts & Components”, JIS D4207, Tyre Valves for Automobiles, pp. 1400–1408).
Other vehicle tire valves heretofore used include clamp-in valves. In the case of mounting of a clamp-in valve, an end portion of the valve stem is passed through a valve hole of a wheel from the inside of the wheel, and the valve stem is fixed in the valve hole of the wheel by a valve nut fitted from the outside of the wheel.
In a case where the valve stem is mounted in a valve hole by using an automatic mounting machine, the above-described operation is performed by the automatic mounting machine while the base end of the valve stem is held by a jig.
Japanese Laid-Open Patent Publication No. 2000-81358 discloses a wireless-communication-type tire condition monitoring apparatus for checking the conditions of tires mounted to a vehicle from the interior of the vehicle. The tire condition monitoring apparatus has a plurality of transmitters attached to wheels in combination with the tires, and a receiver provided on a body of the vehicle. Each transmitter measures the conditions of the corresponding tire including the air pressure and the temperature in the tire to obtain data indicating the measured tire conditions, and transmits the data to the receiver by wireless communication. A casing for accommodating the transmitter is provided on the base end of the valve stem.
There has been a problem that when the valve stem provided with the casing is mounted in the valve hole by an automatic mounting machine, the base end of the valve stem cannot be held by a jig because the casing obstructs holding of the valve stem by the automatic mounting machine.